Different forms of signal information, such as audio information, video information, and electronic data processing programs and data, are routinely recorded in the form of information-containing surface relief images. The signal information is recorded in various types of information-containing signal formats, such as analog signal formats or digital signal formats, depending on the method to be used to reproduce the recorded information.
Various methods have heretofore been used for transcribing signal information in the form of a surface relief image into a recording medium. One of the earliest methods was to form the surface relief image in a wax or lacquer recording medium using a heated stylus. The heated stylus method is marginal for conventional records and was also found to be totally unsatisfactory for high density information discs because of the low resolution and poor signal-to-noise ratios of the recorded information.
Later, an electron beam was used to record information-containing surface relief patterns in a recording medium comprised of an electron beam resist. Electron beam recording presents difficulties in consistently producing high resolution surface relief images with the high signal-to-noise ratios required for high density information because of variations encountered in the electron beam resists and in the development of the exposed resists.
A laser beam has also been used to record information into a laser-sensitive recording medium. Laser recording is also difficult to implement. Laser-recorded surface relief images tend to be highly irregular at the outer edges of the signal track which reduces the resolution capability and causes problems in replicating laser recorded media.
Mechanically micromachining a surface relief image into an electrodeposited metal substrate has also been used. This method was disclosed by G. J. Halter in U.S. Pat. No. 4,044,379 entitled "Method And Apparatus For Electromechanical Reproduction of Short Wavelength Modulation In A Metal Master," the disclosure of which is incorporated by reference. The mechanical micromachining method disclosed by Halter was found to be satisfactory for recording media for both conventional records and high density information discs. The surface relief images which were obtained under ideal conditions had exceptionally high signal resolution, excellent signal-to-noise ratios, and the recorded metal substrates could be readily reproduced numerous times using conventional matrixing methods as opposed to the recorded media formed by the heated stylus method, electron beam recording, and laser recording, which could only be used to form a single replica.
Certain problems, however, were encountered with the metal recording medium used in the mechanical micromachining method disclosed by Halter. The recording medium of Halter is prepared by electrodepositing bright acid copper on a suitable supporting substrate. It was found that the electrodeposition process had to be very closely controlled to obtain electrodeposited copper with the satisfactory properties for mechanical micromachining. However, even under what apparently were ideal electrodeposition conditions, substrates were often obtained which had properties which were not totally satisfactory for use as recording media using the Halter method.
It would be highly advantageous to obtain a recording medium which can be consistently produced having the required properties for mechanical micromachining.